1. Field of the Invention
The present invention relates generally to chemical mechanical planarization (CMP) methods and systems, and more particularly, to a belt wiper for removing fluid and particulate material that can interfere with a CMP process.
2. Description of the Related Art
In the fabrication of semiconductor devices, planarization operations on silicon wafers, which can include planarizing, polishing, buffing, and cleaning, are often performed. Typically, integrated circuit devices are in the form of multi-level structures on silicon substrate wafers. At the substrate level, transistor devices with diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. Patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric and metal layers increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography.
Planarizing metallization layers is becoming more important due to replacement of aluminum with copper as the metal of choice for metallization processes. One method for achieving semiconductor wafer planarization is the chemical mechanical planarization (CMP) technique. Further applications include planarization of dielectric films deposited prior to the metallization process, such as dielectrics used for shallow trench isolation or for poly-metal insulation. CMP systems typically implement a rotary, an orbital, or a linear pad system in which a preparation surface of a polishing pad is used to polish one side of a wafer. In general, the CMP process involves applying a controlled pressure to a typically rotating wafer that is in contact with a moving polishing pad coupled with a slurry containing a mixture of abrasive materials and chemicals to facilitate the planarization process. Slurry is most usually introduced onto a moving preparation surface and distributed over the preparation surface as well as the surface of the semiconductor wafer being prepared by the CMP process. The distribution of the slurry is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the fluid dynamics between the semiconductor wafer and the preparation surface.
FIG. 1 shows a conventional linear belt-type CMP system 100. The conventional linear belt-type CMP system 100 includes a polishing head 108, also known as a wafer carrier, which secures and holds a wafer 104 in place during CMP processing. A belt pad 102, also known as a linear polishing belt, is disposed in the form of a band around rotating drums 112. The belt pad 102 is composed of materials that provide structural integrity and facilitate the planarization/polishing of the CMP process. The belt pad 102 moves in a direction 106 at a speed of up to approximately 1000 feet per minute; however, this speed may vary depending upon the specific CMP process. As the belt pad 102 moves, the polishing head 108 rotates and lowers the wafer 104 onto the top surface (i.e., the preparation surface) of the belt pad 102. The wafer 104 is applied to the belt pad 102 with a force 118 sufficient to facilitate the CMP process.
A fluid bearing platen manifold assembly 110 supports the belt pad 102 during the CMP process. Typically, the fluid bearing platen manifold assembly 110 utilizes a pressurized gas bearing. The pressurized gas bearing, typically composed of clean dry air, is provided by a gas source 114 and is input through the fluid bearing platen manifold assembly 110 via several independently controlled dispersion holes. The pressurized gas bearing provides upward force on the belt pad 102 to control the profile of the belt pad 102.
A slurry 122 is delivered to the belt pad 102 by a slurry manifold 120 including many nozzles. The slurry manifold 120 dispenses the slurry 122 on the top surface of the belt pad 102. Movement of the belt pad 102 in the direction 106 transports slurry 122 underneath the wafer 104. The slurry manifold 120 is typically aligned in a position relative to the wafer 104 such as center on the wafer 104. However, the position of the slurry manifold 120 can be adjusted to somewhat optimize the uniformity of the removal of material from the surface of the wafer 104.
A pre-wet manifold 124 containing a number of dispersion holes 126 is positioned at a leading edge of a platen assembly 135, where the leading edge is defined relative to the belt pad 102 movement direction 106. A fluid, typically deionized water, flows through the dispersion holes 126 of the pre-wet manifold 124 to provide both rinsing and lubrication of the underside of the belt pad 102 and the fluid bearing platen manifold assembly 110. Prior to reaching the pre-wet manifold 124, the edge of the belt pad 102 passes by a belt-tracking sensor 128. The belt-tracking sensor 128 is used to sense the position of the belt pad 102 edge so that the belt pad 102 can be steered accurately while traveling around the rotating drums 112 in the direction 106.
FIG. 2 shows a top view of the platen assembly 135. The platen assembly 135 includes the fluid bearing platen manifold assembly 110. Pressurized gas flows out of a number of dispersion holes 136 to provide support and lubrication to the belt pad 102 as it traverses the platen assembly 135. Also, a platen optics window 130 is located at the center of the fluid bearing platen manifold assembly 110. The platen optics window 130 is a component of an endpoint detection system which measures a wafer film thickness and signals when the CMP process is finished. The pre-wet manifold 124 containing the number of dispersion holes 126 is also shown attached to the leading edge of the platen assembly 135 with respect to the belt pad 102 direction 106.
FIG. 3 shows a top view of the belt pad 102 traversing the pre-wet manifold 124 and the platen assembly 135 in the direction 106. The belt pad 102 contains a belt window 132 which passes over the platen optics window 130 as the belt pad 102 traverses the platen assembly 135. The belt-tracking sensor 128 is also shown in relation to the belt pad 102 edge and platen assembly 135. By monitoring a distance across a region 134 between the belt-tracking sensor 128 and the belt pad 102 edge, the belt pad 102 can be accurately steered as it travels around the rotating drums 112.
The belt-tracking sensor 128 operates based on sound wave propagation and detection. The belt-tracking sensor 128 generates and directs sound waves toward the belt pad 102 edge. The sound waves are reflected back from the belt pad 102 edge to the belt-tracking sensor 128 where they are detected. A propagation time required for the sound waves to travel to the edge of the belt pad 102 and return to the belt-tracking sensor 128 is used to accurately determine the position of the belt pad 102 edge. The sound wave propagation time can be affected by variations in the region 134 through which the sound wave travels. Normally, the belt pad 102 edge position is determined using the sound wave propagation time and assumptions regarding the prevailing characteristics of the region 134 between the belt-tracking sensor 128 and the belt pad 102 edge. During a CMP process, air from the fluid bearing platen manifold assembly 110 blows through both the fluid provided by the pre-wet manifold 124 and any excess slurry 122 on the underside of the belt pad 102 resulting in a disturbance of the region 134 between the belt-tracking sensor 128 and the belt pad 102 edge. The air, fluid, and slurry 122 disturbance causes a change in the density of the region 134 resulting in a corresponding change in sound wave propagation velocity within the region 134. Therefore, the assumptions regarding the prevailing characteristics of the region 134 combined with the actual sound wave propagation time as measured by the belt-tracking sensor 128 will result in an erroneous determination of the belt pad 102 position. An inability to correctly determine the position of the belt pad 102 prohibits effective belt pad 102 steering. Thus, a problem with the prior art is belt pad 102 steering inaccuracies caused by the intrusion of air, pre-wet fluid, and slurry 122 into the region 134 between the belt-tracking sensor 128 and the belt pad 102 edge.
As previously discussed, the platen optics window 130 and belt window 132 are components of the endpoint detection system used to determine when a CMIP process is completed. Completion of a CMP process is determined by performing an active interrogation of the wafer 104 surface to determine if the desired wafer 104 surface condition has been achieved. The active interrogation in performed using an optical method wherein light is pulsed from an optical device in the platen optics window 130 toward the surface of the wafer 104. The light pulse reflects off the wafer 104 toward the platen optics window 130. The characteristics of the reflected light are used to determine the condition of the wafer 104 surface. When the wafer 104 surface condition achieves the desired results the CMP process is terminated. The belt window 132 allows the light pulse to travel from the platen optics window 130 to the wafer 104 surface and back to the platen optics window 130 to be analyzed. A problem with the prior art is that during the CMP process, slurry 122 and fluid cause both the platen optics window 130 and belt window 132 to become obscured such that the intensity of the light pulse used for endpoint detection is adversely affected.
In view of the foregoing, there is a need for an apparatus and method that can be implemented in a CMP process to prevent belt pad 102 steering inaccuracies caused by the intrusion of air, fluid, and slurry 122 into the region 134 between the belt-tracking sensor 128 and the belt pad 102 edge. Furthermore, there is a need for an apparatus and method that can be implemented in a CMP process to prevent the platen optics window 130 and belt window 132 from becoming obscured by slurry 122 and fluid such that optical endpoint detection is not adversely affected.
Broadly speaking, the present invention fills these needs by providing apparatuses and methods for a belt wiper that can be used in a linear belt-type chemical mechanical planarization (CMP) system to maintain a belt pad in a manner that preserves the functionality of both a belt pad steering system and an endpoint detection system. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several embodiments of the present invention are described below.
In one embodiment, a linear belt-type CMIP system is disclosed. The linear belt-type CMP system includes a first drum and a second drum. A belt pad having a width, a preparation surface, and an undersurface is configured around the first drum and the second drum. As the first drum and second drum rotate, the belt pad moves linearly. A platen provides support at a wafer preparation location where a wafer contacts the belt pad preparation surface during a CMIP process. More specifically, the wafer preparation location is located between a first platen side and a second platen side. The belt pad is configured to traverse over the wafer preparation location in a direction from the first platen side to the second platen side. The first platen side contains a plurality of delivery holes through which a gas is delivered to condition the undersurface of the belt pad prior to traversing the platen. The second platen side contains a plurality of delivery holes through which a liquid is delivered to condition the undersurface of the belt pad after traversing the platen. A wiper blade is positioned between the first drum and the second drum and inside of the belt pad. The wiper blade is configured to extend across width of the belt pad and to be in contact with the undersurface of the belt pad. In this configuration, the wiper blade is capable of removing fluid and particulate material from the underside of the belt pad. The wiper blade is generally configured to remove fluid and particulate material from the undersurface of the belt pad at a position next to the wafer preparation location. In a preferred embodiment, the wiper blade is attached to the first platen side. However, in other embodiments a plurality of wiper blades may be utilized and configured to contact the undersurface of the belt pad at an arbitrary number of positions between the first drum and second drum and inside the belt pad. The wiper blade can be configured to contact the undersurface of the belt pad in either a perpendicular or non-perpendicular manner. The wiper blade further includes a gutter that is configured to flow fluid and direct particulate material removed by the wiper blade toward each of the gutter ends. The gutter ends are formed to direct a flow of fluid and particulate material away from the gutter and away from the belt pad.
In another embodiment, a belt wiper assembly for use in a CMP system is disclosed, wherein the CMP system includes a linear polishing belt having a preparation surface and an undersurface. The belt wiper assembly includes a support body disposed within the linear polishing belt, a bracket attached to the support body, and a blade attached to the bracket. The bracket includes a gutter that is configured to extend across the width of the linear polishing belt. The ends of the gutter can be notched if necessary to direct a flow of fluid and particulate material. The blade is configured to contact the undersurface of the linear polishing belt in either a perpendicular or non-perpendicular manner. The blade contacting the undersurface of the linear polishing belt is flexible and can be shaped to enhance removal of fluid and particulate material.
In yet another embodiment, a method for maintaining an underside of a linear polishing belt of a CMP system is disclosed. Generally speaking, the method includes moving the linear polishing belt while wiping the underside of the linear polishing belt. More specifically, a wiping operation is performed prior to movement of the linear polishing belt over a wafer preparation location. Following the wiping operation, a drying of the underside of the linear polishing belt is performed prior to movement of the linear polishing belt over the wafer preparation location. Once the linear polishing belt moves over the wafer preparation location, a wetting of the underside of the linear polishing belt occurs. In alternate embodiments, numerous wiping operations are implemented using a plurality of wiper blades configured to contact the undersurface of the linear polishing belt at an arbitrary number of locations.
The advantages of the present invention are numerous. Most notably, the use of the belt wiper in the CMP system as disclosed in the present invention avoids the problems of the prior art by providing a device and method for preventing belt pad steering inaccuracies caused by the intrusion of air, fluid, and slurry into the region between the belt-tracking sensor and the belt pad edge. Furthermore, the use of the belt wiper in the CMP system provides a device and method that prevents the platen optics window and belt window from becoming obscured by slurry and fluid such that optical endpoint detection is adversely affected.
Other aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the present invention.